DE112006003208T5 - Method and apparatus for combustion control in a multi-cylinder engine with homogeneous compression ignition - Google Patents

Abstract

A method of controlling combustion in a multi-cylinder internal combustion engine operating in a controlled auto-ignition mode, comprising:
monitoring combustion in each cylinder;
determining a target value of a combustion phasing; and
selectively controlling a fueling to each cylinder that causes the target phasing of the combustion phasing to be achieved.

Description

TECHNICAL AREA

These This invention relates generally to control systems of internal combustion engines and more particularly, operating an engine with homogeneous compression ignition.

BACKGROUND OF THE INVENTION

In order to improve the thermal efficiency of a gasoline internal combustion engine, dilute combustion - either by air or by means of recirculated exhaust gas - increases thermal efficiency and reduces NO _x emissions. However, due to misfire and combustion instability due to slow burning in one or more cylinders, there is a limit to which an engine may be operated with a dilute mixture. Known methods for extending the dilution limit include 1) improving ignitability of the mixture by improving ignition and fuel preparation, 2) increasing the flame speed by introducing charge motion and turbulence, and 3) operating the engine using a combustion process with controlled auto-ignition.

The controlled auto-ignition process is also referred to as the homogeneous compression ignition (HCCI) process. In this process, a mixture of combusted gases, air and fuel is generated, referred to as a combustion charge, and auto-ignition is triggered simultaneously in the mixture during compression at many ignition sites, resulting in stable power output and high thermal efficiency. Since the combustion is highly diluted and evenly distributed throughout the combustion charge, the temperature of the burned gas and thus the NO _x emissions are significantly lower than NO _x emissions of a conventional spark engine based on propagating a flame front and a conventional diesel engine, which is based on an attached flame diffusion. A combustion phasing is an important aspect of the combustion process and includes timing of a cylinder's internal combustion parameter relative to piston position and is typically measured by a rotational angle of a crankshaft. In-cylinder combustion parameters include such parameters as a peak pressure (LPP) location and an engine crank angle at which 50% of a combustion charge is burned (CA-50).

Engines, operated with a combustion with controlled auto-ignition be, hang on Factors that determine the composition, the temperature and the Include pressure of the cylinder charge at the closing of the intake valve, to control the combustion phasing. Therefore, the Control inputs to the engine, such as the mass and the Time of fuel injection (relative to the piston position) and the intake / exhaust valve profiles, carefully matched become a robust auto-ignition combustion to ensure. Generally speaking, a HCCI engine for the best fuel economy unthrottled and operated with a lean air / fuel mixture.

at a HCCI engine, which has a valve strategy of exhaust recompression used, the temperatures of the combustion charge in each Cylinder controlled by hot Residual gas from a previous combustion cycle during a Period of a negative valve overlap (NVO) is captured. The NVO period is considered one by one Engine crank angle defined area defined in the both the intake as well as the exhaust valve for a given cylinder are closed and occurs around the TDC inlet. While everyone Inlet phase of a combustion cycle occurs recompression during a NVO period by advancing the closing (i.e., earlier closing) of an exhaust valve , preferably in combination with delaying the opening (i.e., late opening) of a corresponding inlet valve, preferably symmetrically around the upper Dead center (TDC). Both the composition and the temperature the combustion charge will be due to the closing time of the exhaust valve strongly influenced. In particular, by an earlier closing of the Exhaust valve more hot Residual gas retained from a previous combustion cycle what less space for an incoming mass of fresh air leaves. The net results include a higher one Temperature of the combustion charge and a lower oxygen concentration the combustion charge. The controlled use of the NVO leads to a Possibility, the amount of hot Control residual gas trapped in each cylinder. During each NVO period can be injected with an amount of fuel and in the Be reformed combustion chamber.

at a HCCI engine with multiple cylinders, the combustion phasing between individual Cylinders due to differences in the thermal boundary conditions the single cylinder and differences in inlet conditions, including Variations in the air intake, the fuel injection, the recirculated exhaust gases and the spark, vary considerably.

It is known, the combustion phase position by means of additional Heat too controlled by the fuel reforming process, about the temperature of the cylinder charge and the combustion phasing to change. Excessive fuel reforming elevated However, fuel consumption, and therefore it is advantageous to one Control scheme to design a balance between cylinders with minimal errors in the combustion phase by means of a lowest amount of fuel reforming achieved.

It there is a need for a system that improves the performance of a HCCI engine while the concerns described above.

SUMMARY OF THE INVENTION

Therefore be in accordance with a embodiment the invention provides a method and a device to to control combustion in a multi-cylinder internal combustion engine, operated in a controlled auto-ignition mode. This includes monitoring combustion in each cylinder and determining a target value the combustion phase position. A fuel supply to each cylinder is selectively controlled so that the target value of the combustion phase position is achieved and that the achievement of the target value of the combustion phase position further controlling the fuel supply such that the combustion phasing the cylinder is brought into balance.

These and other aspects of the invention will become apparent to those skilled in the art if they are the following detailed description of the embodiments read and understand.

BRIEF DESCRIPTION OF THE DRAWINGS

The Invention may be in certain parts and in an arrangement of parts take physical form, the embodiment of which described in detail and shown in the attached drawings below, comprising:

1 is a schematic representation of a control scheme according to the present invention; and

2A and 2 B are data graphs according to the present invention.

DETAILED DESCRIPTION OF ONE Embodiment THE INVENTION

Referring now to the drawings, the figures are only for the purpose of illustrating the invention and not for the purpose of limiting the same 1 a schematic representation of a control scheme for controlling an internal combustion engine 10 , constructed in accordance with an embodiment of the present invention. The control scheme includes control logic, preferably as at least one algorithm in the control module 5 is executed and which serves to control an aspect of the overall engine operation. The electronic control module monitors and processes a variety of inputs from the engine 10 and acts to control one or more engine actuators, all based on the control logic.

Although not shown in detail, it will be appreciated that the present invention can be applied to a multiple-cylinder four-stroke direct injection internal combustion engine that can be operated with a controlled auto-ignition process, that is, the aforementioned homogeneous compression ignition or HCCI. The construction of the engine preferably comprises a conventional internal combustion engine having a plurality of cylinders closed at one end, each cylinder closed at one end having a movable piston inserted therein defining, together with the cylinder, a variable volume combustion chamber. An inlet port supplies air to the combustion chamber, wherein the flow of air into the combustion chamber is controlled by one or more inlet valves. Burnt (spent) gases flow out of the combustion chamber through an exhaust port, with the flow of the burned gases through the exhaust port being controlled by one or more exhaust valves. A system for controlling the opening and closing of the intake and exhaust valves may include means and control strategies that control the magnitude of the valve lift or valve opening, the duration of the valve opening, and the timing of valve opening, and typically include intake valves and / or exhaust valves for all engine cylinders , A crankshaft is connected by a connecting rod to each piston which reciprocates in each cylinder during ongoing engine operation. The engine is preferably equipped with an ignition system that includes a spark plug inserted into the respective combustion chamber. A crankshaft sensor monitors the rotational position of the crankshaft. A fuel injector serves to inject fuel directly into each combustion chamber and is controlled by the control module 5 controlled. The fuel injector is controllable in a single injection mode or a split injection mode. In the split injection mode, during each combustion cycle, there is a first event of fuel injection that is for a force fuel reforming, and a second major event of fuel injection that may be used to drive the engine. In the described embodiment, each cylinder has a cylinder pressure sensor to monitor the cylinder's own pressure during operation. The information of the cylinder pressure sensor is used in the control scheme to identify specific combustion characteristics, such as the location of the peak cylinder pressure. It will be understood that alternative devices and methods that monitor and determine specific combustion parameters may be used in the invention by the control scheme. Alternative means and methods include, for example, monitoring a spark ionization current and monitoring a change in crankshaft speed, both of which serve to provide parameters that are correlatable to the combustion phasing. The engine is preferably equipped with dual-variable variable cam phasing control means which controls the opening and closing operations of the intake and exhaust valves. The variable cam phaser is controlled by the control module 5 controlled and operated by an electro-hydraulic, a hydraulic or an electric actuator of the cam phaser.

The Combustion phasing may occur during of engine operation with controlled auto-ignition by adjusting an overlap intake and exhaust valves, including a negative valve overlap (NVO), and other engine operating parameters, such as mass and the time of injection, the ignition timing, the throttle position and the position of an EGR valve. The NVO amount can by means of many mechanisms are set, for example by means of a fully flexible valve actuation system (FFVA system), of the above Dual-equal system of cam phasing and a mechanical two-stage valve system. The negative valve overlap (NVO) acting as a Crank angle duration is defined in which both the intake and also the exhaust valve for a given cylinder is closed, occurs during a Period of time, when a certain piston during an inlet portion of each engine cycle reaches top dead center (TDC inlet). NVO is used in the present invention to control the amount of hot residual gases to control that is trapped in the cylinder.

The Combustion phase of the exemplary multi-cylinder engine is influenced by the throttle valve position and EGR valve positions whose Impact for all cylinders are holistic. Therefore, the control of the throttle valve position and the control of the EGR valve position is not effective to the Controlling the combustion phase position of a single cylinder.

A Control of the fuel injection is necessary to one self ignited Combustion over to achieve a wide range of engine loads. For example can a combustion charge at a low engine load (eg. Fuel rate <7 mg / cycle at 1000 rpm) for a stable self-ignited Burn not hot enough be the highest practical value of NVO is used, resulting in partial combustion or a misfire the combustion charge leads. The temperature of the combustion charge can be controlled by a pre-injection a small amount of fuel near the TDC inlet during a Recompression and the NVO are increased, resulting in a fuel reforming leads, d. H. the fuel is in a mixture of hydrogen, CO and light HC molecules transformed. At least part of the pre-injected fuel reforms due to high pressure and high temperature while the recompression. The output by the fuel reforming Thermal energy Helps to heat loss due to a transfer the engine heat and evaporation of the liquid fuel balance, and increased the temperature of the cylinder charge sufficiently to the combustion charge to light yourself, during a subsequent main fuel injection event is generated. The amount of pre-injected fuel that accumulates during the Reforming reformed depends from many variables, such as the injected mass, the injection time and the temperature and pressure of the trapped Exhaust gas. The heat output from the fuel reforming process can be used to to change the temperature of the cylinder charge by either the injection timing or Controlled the amount of fuel injection during the NVO period become. This will cause HCCI combustion controlled, and it follows a second, a main fuel injection. In order to maintain fuel economy, it is desirable to minimize the amount of fuel needed for reforming and the Cylinder compensation is used.

As previously described, the control module is 5 Preferably, an element of an overall control system having a distributed control module architecture for providing coordinated control of a powertrain system. The control module 5 assembles appropriate information and inputs from gauges including the crankshaft sensor, cylinder pressure sensors, exhaust gas sensor, and other engine sensors, and performs algorithms to control the operation of various actuators, such as the fuel injector and variable valve actuators in order to achieve operator torque demand and engine operation so as to meet control goals related to factors including emissions, fuel economy, driveability, and others.

The control module 5 is preferably a general-purpose digital electronic computer, which essentially comprises a microprocessor or central processing unit, storage media comprising read only memory (ROM), random access memory (RAM) and electrically programmable read only memory (EPROM), a high speed clock, analog to digital circuits Conversion (A / D) and for digital-to-analog conversion (D / A) and input / output circuits and devices (I / O) as well as suitable signal conditioning and buffer circuits. A set of control algorithms comprising resident program instructions executable by the central processing unit and calibrations are stored in the ROM and executed to provide the respective functions. The algorithms are usually executed during preset loop cycles so that each algorithm is executed at least once per loop cycle. The algorithms stored in the nonvolatile memory devices are executed by the central processing unit and serve to monitor inputs from the measuring devices as well as to execute control and diagnostic routines to control the operation of the respective device by means of preset calibrations. Loop cycles are typically performed during ongoing engine and vehicle operation at regular intervals, for example, every 3.125, 6.25, 12.5, 25, and 100 milliseconds. Alternatively, the algorithms may be executed in response to an occurrence of an event.

Back on 1 Referring to FIG. 1, there is shown a graphical representation of the control scheme including a method and apparatus for controlling combustion phasing to balance combustion between the engine cylinders when the engine of the present invention is in the controlled auto-ignition mode is operated.

During the Operating in the controlled auto-ignition mode, there is a total fuel mass, which is to be injected into each combustion chamber to one Meet torque request of an operator and drive the motor. The combustion phasing, the timing of the cylinder's own Combustion parameter relative to the piston position is controlled in each cylinder by controlling the fuel reforming.

The control scheme operates as follows: the combustion is monitored in each of the cylinders, and combustion parameters from each cylinder are monitored (block 20 ) to determine a parameter of the combustion phasing T ₁ (k), T ₂ (k), ..., T _j (k) for each of the j cylinders during each engine cycle k. In this embodiment, a pressure in the cylinder is monitored for each cylinder as a function of a crank angle. Monitoring combustion includes determining a combustion operating parameter for each cylinder during each engine cycle, including, for example, an engine crank angle at which a combustion pressure in the cylinder reaches a peak pressure, commonly referred to as a peak pressure (LPP) location. Alternatively, the monitoring of the combustion includes an engine crank angle at which 50% of a combustion charge is burned (CA-50). Other combustion parameters are applicable that use other monitoring schemes.

A target value of the combustion phase position T _{T is} determined, which is preferably selected from the parameters of the combustion phase position T ₁ , T ₂ ,... T _j , which are determined during each engine cycle (block 22 ). The selected target combustion phasing T _T further includes a phasing achievable by each cylinder by means of fuel reforming. The logic used to select the target combustion phasing value in an engine cycle k, T _T (k) is shown in Equation 1 as follows: T T (k) = min {T n (K) | I n (k) <ε}, [1] where T _n (k) is the combustion phasing of the n-th cylinder in the engine cycle k, I _n (k) is the integrator value of the integral controller for the n-th cylinder in the engine cycle k and ε is an adjustable parameter. The parameter ε is usually calibrated to represent a sufficiently small positive number. The value I _n (k) is directly related to the amount of fuel reform required by the controller to reach an actual combustion phasing T _n that approaches T _T. The relation for the integrator parameter is I _n (k) ≥ 0 for all n and k. When the target value of the combustion phasing T _{T is} achievable, each of the integrals I _n converges when T _n approaches T _T. Each engine event T _n and T _T is determined during each engine cycle, and an error e _n is determined as a difference between the values. Each error e _n is added to a previous value of the integrator I _n arithmetic, to determine a new value for _n I (block 24 ). The target value of the phase position T _T is output to an overall controller for the combustion phase position, the preferential wise in the control module 5 resides to determine command parameters for the NVO, EGR, throttle, and mass and timing of fuel injection, including both the first event of the fuel injection and the main event of fuel injection when operating in the split injection mode takes place (block 26 ). The fuel reforming process increases the cylinder temperature and thus introduces the combustion phasing. The combustion phasing of one of the cylinders having a most advanced combustion phasing at a least amount of fuel reforming is selected as the target combustion phasing value such that the other cylinders achieve the combustion phasing target with a least amount of combustion phasing Can achieve fuel reforming. Under an operating condition in which the target value of the combustion phasing is unavailable, the errors between the target combustion phasing position and the other combustion phasing are preferably minimum for at least one of the cylinders, even with maximum fuel reforming at the least amount fuel reforming.

The cylinder control scheme preferably works with the overall combustion phasing controller (block 26 ) to guide the target value of the combustion phasing T _T to the desired value of the combustion phasing T _d based on an error between these two values. The command parameters for the mass and timing of the fuel injection that are output from the controller (Block 26 ) are set by the integrator I _n to generate commands for controlling the individual fuel injectors, in accordance with the timing of each injection event and the mass of fuel injected during each injection event (Block 28 ).

Either the amount or timing of the first fuel injection is controlled for each cylinder by a single integral controller to minimize the difference between a measured combustion phasing and the target combustion phasing. The amount of fuel supplied is usually adjusted by controlling the pulse width of the injector, and the timing of the injection is usually controlled based on control of a start or an end of each injection event relative to an engine crank angle and a piston position. The individual integrators I _n are always greater than or equal to zero and are limited by a maximum value for all engine events. The target value of the combustion phasing may be guided to the desired combustion phasing by adjusting other actuators by acting on the control module, including adjusting the crank phasing to adjust the NVO, EGR flow, and throttle. Thus, if the target combustion phasing value is achievable for all cylinders, the combustion phasing of each cylinder converges to the desired combustion phasing.

Now up 2A and 2 B Referring to FIG. 12, results from a simulation operation of the exemplary HCCI engine are shown at an engine speed of 1000 rpm. The cylinder balance control scheme is actuated after approximately 10 seconds of operation, as shown. The results represent a peak pressure (LPP) location for each of the four cylinders which, after only a few seconds of operation, approaches a target value of the LPP when the control scheme operates as described above. The corresponding integrator values I _n are for each of the n cylinders in 2 B shown.

The Control scheme provides a method for selecting a target value of the combustion phasing and for calculating an appropriate amount of fuel reforming, by a difference in combustion phasing between the cylinders to reduce. In the control scheme is the setting of a single Cylinder limited, and the difference in the combustion phase position between the cylinders decreases with a minimum amount of fuel reforming a minimum amount. The control scheme determines and controls the Time of the first fuel injection to the level of fuel reforming in each cylinder to adjust the difference in combustion phasing between the cylinders to reduce. Alternatively determined and controlled the control scheme a while of the first injection event to be injected fuel mass, to adjust the level of fuel reforming in each cylinder by the difference in combustion phasing between the cylinders to reduce. Alternatively, in the control scheme, both the Controlled fuel mass as well as the time of the first injection event, to adjust the level of fuel reforming in each cylinder by the difference in combustion phasing between the cylinders to reduce. The example shown uses in one mode split injection only the time of the first fuel injection. It is understood that the same algorithm in each cycle as well applied to a single event of fuel injection can be, with the timing of the injection event controlled and the injected fuel is sufficient to a certain extent Reach the level of reforming and drive the engine.

The advantages of operating an engine in the manner described herein during the HCCI mode include improved engine stability, ie, decreasing the COVIMEP (variation coefficient of indicated mean pressure). This can be used to increase the operating range of the HCCI mode, resulting in improved engine efficiency and fuel economy of the vehicle. Another advantage includes reducing the output by the engine NO _x emissions, thus leading to a broader usability of the HCCI technology.

The present invention provides a fuel injection strategy, which brings cylinder into a balance and the combustion phase position of individual Cylinder adjusts to substantially evenly timed Combustion events in each of the cylinders during operation in the Controlled auto-ignition mode to reach. By the timing of the injection or the amount the fuel injection during the first reforming event of fuel injection, which occurs in the NVO period, can control the heat output from the fuel reforming process used to the temperature to change the cylinder charge. This is preferably followed by the second, main event of fuel injection. The method may also be based on a single fuel injection be applied by adjusting the timing of the injection is about the fuel reforming process and the combustion phasing to control.

The Combustion phasing is in the present invention for each Cylinder of multi-cylinder HCCI engine individually by means of fuel reforming controlled. This reduces the difference in combustion phasing between the cylinders and improves the combustion stability during the HCCI operation. The algorithm achieves a cylinder equalization with a minimal amount of fuel reforming, creating a Fuel economy performance, which is characteristic for HCCI engines is, is maintained.

The The invention has been made with particular reference to the embodiments and their modifications are described. The special details of the Control schemes and the associated results described herein illustrate the invention described by the claims. Further modifications and changes can other people during of reading and understanding the description stand out. It is intended, that all these modifications and changes are included, insofar as they are within the scope of the invention.

Summary

One Method and apparatus are provided for combustion in a multi-cylinder combustion engine operating in one mode with controlled auto-ignition with a minimum error of combustion phasing using a minimum amount of fuel reforming is operated. This includes monitoring combustion in each cylinder and determining a target value the combustion phase position. A fuel supply to each cylinder is selectively controlled so that the target value of the combustion phase position is achieved and that the achievement of the target value of the combustion phase position further controlling the fuel supply such that the combustion phasing the cylinder is brought into balance.

Claims (21)

Method for controlling combustion in a Multi-cylinder combustion engine operating in a controlled mode self-ignition is operated, comprising: a monitoring of a combustion in every cylinder; determining a target value of a combustion phasing; and selectively controlling a fueling to each cylinder, which causes the target value to reach the combustion phasing becomes. The method of claim 1, wherein monitoring combustion in each cylinder, determining a phase position a combustion event in each cylinder. The method of claim 2, wherein determining the Phase of a combustion event in each cylinder further determining a location of a peak cylinder pressure in each cylinder while of the combustion event. The method of claim 2, wherein determining the Phase of a combustion event in each cylinder further determining a crank angle position at which fifty percent of a combustion charge burned off in each cylinder during the combustion event includes. The method of claim 1, wherein determining a Target value of the combustion phase position selecting a most advanced Combustion phasing includes one of the cylinders in each cylinder by means of a Fuel reforming is achievable. The method of claim 1, wherein the selectively Controlling the fueling to each cylinder that causes the target combustion phasing value to be achieved further comprises controlling the fueling that causes the combustion phasing of the cylinders to be balanced. The method of claim 6, wherein controlling the Fuel delivery further comprises: executing a split mode Fuel injection and controlling a first fuel injection such that the injected fuel is substantially reformed. The method of claim 7, further comprising controlling the first fuel injection includes substantially while a period of negative valve overlap occurs. The method of claim 7, wherein controlling the first event of the fuel injection that causes the injected fuel is substantially reformed Controlling a fuel mass includes during the first fuel injection is injected. The method of claim 7, wherein controlling the first event of the fuel injection that causes the injected fuel is substantially reformed Controlling a fuel mass and a time of the first fuel injection includes. The method of claim 6, wherein controlling the Fuel delivery further comprises: performing a single fuel injection such that a portion of the injected fuel reforms and the motor is driven. Method to combustion in a multi-cylinder internal combustion engine to balance, comprising: a monitor combustion in each of the cylinders during operation in one Controlled self-ignition mode; one Choose a target value of a combustion phasing for all cylinders; a run of a first fuel injection event in each cylinder, the one selectively controlling a time or mass of the fuel supply includes; and a run a second fuel injection event in each cylinder, this causes a torque request of an operator in the Essentially fulfilled becomes. The method of claim 12, wherein performing the the first fuel injection event in each cylinder selectively controlling a time or mass of the fuel supply such that the combustion phase position of the cylinder in a balance is brought. The method of claim 13, further comprising performing the based on the first fuel injection event in each cylinder on the target value of the combustion phasing for combustion in the cylinder includes. The method of claim 13, wherein performing the first fuel injection event, controlling the first fuel injection event such This essentially covers a period of time negative valve overlap occurs. The method of claim 15, further comprising controlling of the first fuel injection event such that the injected fuel is substantially reformed. The method of claim 12, wherein selecting the Target value of the combustion phase position for the combustion in the cylinder selecting one most advanced combustion phasing of one of the cylinders comprising, by means of a fuel reforming by each cylinder is reachable. Device containing a storage medium with a machine-executable Code encoded in this and a control of a Combustion in a multi-cylinder internal combustion engine causes the code includes: a code for monitoring combustion in every cylinder during an operation in a controlled self-ignition mode; one Code for determining a target value of the combustion phasing; and one Code for selectively controlling fuel delivery to each cylinder such that the target value of the combustion phase position is achieved and the combustion phasing of the cylinders in an equilibrium is brought. The apparatus of claim 18, wherein the code is for monitoring combustion includes: a code for monitoring an engine combustion pressure, around for each combustion chamber has a combustion phasing during one To determine operation in the controlled auto-ignition mode. The apparatus of claim 18, wherein the code is for monitoring combustion includes: a code for monitoring a speed change a crankshaft in order for each combustion chamber has a combustion phasing during operation in the Controlled auto-ignition mode to determine. The apparatus of claim 18, wherein the code is for monitoring combustion includes: a code for monitoring a spark ionization current, around for each combustion chamber has a combustion phasing during one To determine operation in the controlled auto-ignition mode.